To find the perimeter, you add up the lengths of all the outer sides of a shape.

What perimeter means

Perimeter is the total distance around a 2D shape, like walking all the way around a field or a garden fence.

In symbols we often write it as PPP for perimeter.

General method (works for any shape)

For any polygon (shape made from straight sides):

  • Measure every outside side.
  • Add all those measurements together.
  • Keep the same units (all cm, all m, etc.).

So in general:

  • Perimeter P=P=P= sum of all side lengths.

Example: a 4‑sided plot has sides 3 m, 5 m, 4 m, 6 m.
Perimeter P=3+5+4+6=18P=3+5+4+6=18P=3+5+4+6=18 m.

Common formulas by shape

These are just shortcuts for “add all the sides”.

  • Square (all sides equal, side length aaa):
    P=4aP=4aP=4a.
  • Rectangle (length lll, width www):
    P=2(l+w)P=2(l+w)P=2(l+w).
  • Any triangle (sides a,b,ca,b,ca,b,c):
    P=a+b+cP=a+b+cP=a+b+c.
  • Regular polygon (all sides same, nnn sides, side length sss):
    P=n×sP=n\times sP=n×s.
  • Circle (often called circumference, radius rrr):
    P=2πrP=2\pi rP=2πr.

Irregular shapes

If the shape is not regular (sides all different):

  • Write down every outer side length.
  • Add them one by one; that total is the perimeter.

If part of the boundary is curved (like arcs of circles), find the length of each arc using circle formulas, then add them to the straight sides.

Quick way to remember

A simple way to remember perimeter is: “add all the outer sides together.”

If you tell me the exact shape and its side lengths, I can walk through a specific perimeter calculation step by step.